1. Field of the Invention
The present invention relates generally to stimulating medical devices, and more particularly, to fitting a stimulating medical device.
2. Related Art
Many medical devices have structural and/or functional features which are to be adjusted for an individual recipient. The process by which a medical device is tailored or customized for the specific needs of a recipient is commonly referred to as fitting. One type of medical device which is typically fitted to individual recipients is a cochlear implant system.
Cochlear implant systems provide the benefit of hearing to individuals suffering from severe to profound hearing loss. Hearing loss in such individuals is often due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Cochlear implant systems essentially simulate the auditory nerves by directly delivering electrical stimulation to the auditory nerve fibers. This causes the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered by the auditory nerve.
Conventional cochlear implant systems commonly include an external assembly directly or indirectly attached to the body of the recipient (sometimes referred to herein as the recipient), and an internal assembly which is implanted in the recipient. The external assembly typically comprises one or more microphones for detecting sound, a speech processing unit that converts detected sound into an electrical coded signal, a power source, and an external transcutaneous transfer coil. The internal assembly typically comprises an internal transcutaneous transfer coil, a stimulator unit located within a recess of the temporal bone of the recipient, and an electrode array positioned in the recipient's cochlea. Completely implantable cochlear implant systems having functionally similar components are under development.
In addition to providing electrical stimulation, some cochlear implant systems also include a mechanical stimulation mode of operation. Such so called mixed-mode systems offer rehabilitation by mechanically stimulating a portion of a recipient's auditory pathway, either acoustically or physically. For example, there have been approaches to offer rehabilitation with conventional hearing aids via the application of an amplified acoustic signal to the external auditory canal, or by physically stimulating an ossicle of the middle ear or the inner ear via mechanical or hydromechanical stimulation.
Modern cochlear implant systems provide a wide variety of fitting options that can be customized for an individual recipient. Because recipients are heterogeneous, each recipient requires a different set of parameters to maximize speech reception and recipient satisfaction. The task of the clinical professional, usually an audiologist, is to select a set of parameters, commonly referred to as a parameter map or, more simply, a MAP, that will provide the best possible sound reception for an individual recipient. Because there may be thousands of possible parameter maps, it is impractical for a recipient to experience all of the alternatives and to evaluate the performance of each alternative. Nor is it possible to identify an optimal parameter map by prescription based on a limited set of measurements as is, for example, the case in fitting eyeglasses. Because parameters of cochlear implant systems often interact non-linearly and non-monotonically, it is also not feasible to sequentially optimize individual parameters, adjusting each in succession to its optimal value.
As a result, clinicians have adopted a variety of approaches for fitting the cochlear implant systems to recipients. Some simply set the parameters to default values regardless of the individual recipients. Others adopt preferred parameter maps, which they believe are good, if not best, for many or most recipients. The preferences may be based on personal experience, published performance data, or intuition. Some clinicians evaluate a limited set of alternatives adjusting individual parameters based upon measured perceptual limitations and inferred relationships among the parameters. These approaches are time consuming, costly, and unreliable, and typically fail to achieve the optimal outcome for individual recipients.